: Our long term goals are to study transmembrane signalling by heterotrimeric G proteins. The structure and most molecular aspects of transmembrane signalling G proteins have been solved, but their respective participation in complex homeostatic processes such as inflammatory reactions, pain perception, behavior and maintenance of normal glycemia remains largely unknown. During the previous and this last granting period we began addressing the roles of G proteins in homeostasis by creating mice lacking specific G proteins (knockout mice). We have now individually knocked out four of the 15 G protein alpha subunit genes: Gi1, Gi2, Gi3 and Go, and we also have a double and Gi1/Gi3 knockout. These G proteins form the group of non-sensory pertussis toxin (PTX)-sensitive G proteins which couples a distinct set of receptors to a common set of effectors. Two of the knockouts (Gi1 and Gi3, and their combination) are so far asymptomatic. Gi2-/- mice develop ulcerative colitis (UC) and adeno-carcinomas, but in a context sensitive manner, i.e., depending on the strain (genomic background). Go-/-mice have multiple neurological alterations and term this phenotype 'rotator'. Go-/- mice also show unexpected alterations in Ca2+ channel function and, when subjected to a glucose load, respond with a much tighter control of glycemia than controls. For the coming years we propose: a. To complete the disruption of the Gz G protein, which shares with the inactivated G protein alpha subunits a high degree of structural and functional similarity, coupling the same set of receptors to the same set of effectors, but is PTX- insensitive. This will be complemented by the creation by breeding of the compound G protein deficiencies. b. To search for and characterize one or more genes responsible for suppression (or promotion) of the development of UC and adenocarcinomas in Gi2-/- mice. c. To search for the neurotransmitter system(s) in the CNS affected by lack of Go and, if possible, interpret the rotator phenotype in terms of existing theories of central nervous system motor circuits. And d. to characterize insulin secreting properties of Go-/- islets in vivo and in vitro. The identification of one or more modifier genes of UC and/or adenocarcinoma formation may aid in the elucidation of the etiology of human UC and its complications (adenocarcinomas). Investigation of the role of Gz is expected to shed new light on molecular mechanisms involved in thrombus formation. The elucidation of the mechanism(s) altered by lack of Go may aid in the understanding of human motor disorders and may shed new light on development and/or treatment of type II diabetes.